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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 5  |  Issue : 2  |  Page : 52-58

Effect of obesity on self-reported pain and functional disability in patients with knee osteoarthritis in Zaria, North Western Nigeria


1 Senior Lecturer/Consultant Rheumatologist, Faculty of Clinical Sciences, College of Health Sciences, Ahmadu Bello University Teaching Hospital, Zaria, Kaduna State
2 Professor of Medicine/Consultant Rheumatologist, Department of Medicine, Lagos State University Teaching Hospital, Kaduna State
3 Professor of Medicine/Consultant Pulmunologist, Faculty of Clinical Sciences, College of Health Sciences, Ahmadu Bello University Teaching Hospital, Zaria, Kaduna State
4 Senior Lecturer/Consultant Radiologist, Faculty of Clinical Sciences, College of Health Sciences, Ahmadu Bello University Teaching Hospital, Zaria, Kaduna State

Date of Web Publication1-Nov-2018

Correspondence Address:
AbdulAziz Umar
Department of Medicine, Faculty of Clinical Sciences, College of Health Sciences, Ahmadu Bello University Teaching Hospital, Zaria
Kaduna State
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DOI: 10.4103/ssajm.ssajm_10_18

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  Abstract 


Introduction: Osteoarthritis (OA) is the most common causes of arthritis in human, with the knee joint being the most commonly affected. Knee OA patients often present with knee pain and varying degree of functional limitation in activities of daily living. The incidence and prevalence of knee OA increases with age and is poised to increase even further in tandem with an expected increase in life expectancy, rise in population age, and increased prevalence of obesity. Obesity is associated with the occurrence and severity of knee OA, and it is perhaps the most amenable of all knee OA risk factors. The contribution of obesity to pain and functional limitation in Nigerian knee OA patients is not well elucidated. This study aims at ascertaining the burden of obesity in Nigerian knee OA patients with regards to its prevalence, effects on pain, and functional disability. Materials and Methods: Between January 2010 and February 2011, 140 consenting knee OA patients were recruited consecutively, as they presented to the Rheumatology Clinic of Ahmadu Bello University Teaching Hospital, Zaria. Knee OA was diagnosed in patients using American College of Rheumatology clinicoradiographic criteria. Information was collected from patient using a pretested interviewer-administered structured question. Pain, stiffness, and functional disability were determined using Likert version of Western Ontario McMaster Universities Osteoarthritis index (WOMAC). Patients were grouped based on body mass index (BMI) into obese (BMI > 30 kg/m2) and nonobese (BMI < 30 kg/m2), and differences in pain intensity and functional disability were compared. Results: One hundred and forty knee OA patients comprised 120 females (85.7%) and 20 males (14.3%), with male–female ratio of 1:6. The mean age of patients was 59.6 ± 8.8 years. The mean BMI was 30.5 (±6.4) kg/m2. Twenty-seven (19.3%) patients had normal body weight, whereas 48.6% were obese. Mean duration of knee pain in patients was 3.5 (±2.9) years. Mean pain score and mean disability scores were 2.17 (±0.7) and 2.02 (±0.89), respectively. The mean pain score was higher in obese patients compared to nonobese (2.4 ± 0.78 vs. 1.93 ± 0.59, P = 0.000), and mean disability score was significantly higher in obese patients compared to nonobese (2.58 ± 0.79 vs. 1.78 ± 0.81, P = 0.000). There was moderate correlation between BMI and pain scores (r = 0.56, P = 0.000) and between BMI and functional disability scores (r = 0.5, P = 0.000). BMI was an independent predictor of functional disability. Conclusion: Pain and functional disability are more severe in obese and overweight knee OA patients compared to those with normal BMI, and obesity is an independent predictor of functional disability.

Keywords: Functional disability, knee osteoarthritis, obesity, pain


How to cite this article:
Umar A, Adelowo OO, Okpapi JO, Omuya UB. Effect of obesity on self-reported pain and functional disability in patients with knee osteoarthritis in Zaria, North Western Nigeria. Sub-Saharan Afr J Med 2018;5:52-8

How to cite this URL:
Umar A, Adelowo OO, Okpapi JO, Omuya UB. Effect of obesity on self-reported pain and functional disability in patients with knee osteoarthritis in Zaria, North Western Nigeria. Sub-Saharan Afr J Med [serial online] 2018 [cited 2018 Nov 19];5:52-8. Available from: http://www.ssajm.org/text.asp?2018/5/2/52/243936


  Introduction Top


Osteoarthritis (OA) is the most common rheumatic disease in the general population globally.[1],[2] The prevalence of OA varies widely among populations and depends on diagnostic method employed, which could be clinical, radiographic, or clinicoradiographic criteria. OA of the knees is the most common of all OA and is often associated with disability.[3],[4],[5] The prevalence of knee OA increases steadily with age, and radiographic abnormalities have been noted to occur in more than 30% of persons older than 65 years, with roughly 40% of them being symptomatic.[5] Approximately 19.6% of Nigerian adults have symptomatic knee OA, with prevalence being higher among female—21.4%, compared to 17.5% among males.[3] Given the expected increase in life span and aging of population, as healthcare indices improve, the prevalence and burden of knee OA will likely increase.[6]

Obesity has been linked with the causation of OA in weight-bearing[7],[8] and nonweight-bearing joints.[7],[8] Moreover, for every 1 kg/m2 increase in body mass index (BMI) above 27, the risk of knee OA increases by 15%.[9] OA tends to be more severe in obese individuals compared to those with normal BMI.[9] Figures from World Health Organization (WHO) show that obesity has more than tripled since 1975, with 39% and 13% of adults 18 years and above being overweight and obese, respectively, in 2016.[10] The prevalence of overweight among adult Nigerians is said to be 20.3% to 35.1%, with obesity occurring in 8.1% to 22.2% of the population.[11]

The prevalence of obesity is also likely to rise, given the increase in sedentary life style and changing dietary patterns in populations, thereby placing those affected at risk of development of symptomatic knee OA. Furthermore, higher BMI has been demonstrated to increase the risk of progression of radiographic and thus clinical OA.[12] Although several Nigerian studies have alluded to the high prevalence of functional disability in patients with knee OA, with figures ranging from 41.8% to 90.2%,[3],[13],[14] the contribution of obesity to disease burden has not been explored. Given the increasing prevalence of obesity and the prominent role of obesity as a knee OA causation and severity factor, exploring the effect of obesity on pain and functional disability will be important in tackling the burden of knee OA in Nigerians.


  Materials and methods Top


The study was an observational descriptive study of 140 consecutive patients presenting with knee pain to the rheumatology clinic of Ahmadu Bello University Teaching Hospital (ABUTH) between January 2010 and February 2011. Diagnosis of knee OA was attained using the American College of Rheumatology (ACR) clinicoradiographic criteria.[15] Patients with traumatic and inflammatory arthritis were excluded from the study.

Information obtained from patients using an interviewer-administered validated questionnaire included age, sex, duration of knee pain, knee joint(s) involved. All patients had thorough musculoskeletal examination with emphasis on the knee joints. Anthropometric measurements of weight, height, waist, and hip circumferences were taken using WHO protocol.[16]

BMI was calculated for each patients using the formula weight (kg)/height2 (m2) and classified according to WHO criteria.[17]

For assessment of severity of pain and functional disability, patients were given Likert version of Western Ontario McMaster Osteoarthritis index (WOMAC) to fill. For nonliterate patients, a trained research assistant administered the questionnaire after reading out the content to the patients.

Patients were divided into two groups based on BMI categories into obese (BMI > 30 kg/m2) and nonobese (BMI < 30 kg/m2). Differences in disease presentation and severity were analyzed separately for these two groups.

Knee radiography

All patients had weight bearing radiography of the knees performed and was interpreted by a radiologist unaware of all the information on the participants. Radiographs of the knees were graded according to the Kellgren–Lawrence criteria.[18] Kellgren–Lawrence score of grade 2 and above qualified for radiographic disease. The radiographs of the index knee were used in data analysis.


  Assessment of pain and functional disability using womac osteoarthritis index Top


The WOMAC OA index is a tridimensional, disease-specific, patient-administered health status measure. It probes clinically important, patient-relevant symptoms in the area of pain, stiffness, and physical function in patients with OA of the knee and/or hip. The index consists of 24 questions (five on pain, two on stiffness, and 17 on physical functions) and can be completed in less than 5 min. It is available in Likert (WOMAC LK3.1-series), visual analog (WOMAC VA 3-series), and numerical rating (WOMAC NRS3-series) scaling formats. It is the most widely used assessment tool and has become a standard measure for assessing patients with OA of the knee/hip.[19] The WOMAC index has been shown to have good test–retest reliability and responsiveness,[20] better clinimetric properties compared to other assessment tools,[20],[21] and good face validity for lower limb functions.[22]


  Ethical clearance Top


Ethical approval for this study was obtained from the research and ethics committee of ABUTH Zaria before embarking on the study. Informed voluntary signed consent was sought and obtained from patients before their enrollment into the study.

Statistical method/analysis of data

All information was treated with utmost confidentiality, and data were analyzed using Statistical Package for Social Sciences, version 17 (SPSS Inc., Chicago, Illinois, USA) after screening for outlier and possible wrong entries.
  1. Demographic and baseline characteristics were presented as tables.
  2. Univariate analyses were conducted and presented as range, mean [standard deviation (SD)] for numerical variables, and count/percentages for categorical variables.
  3. Pearson’s correlation coefficient test was used to determine the association between mean WOMAC pain and disability scores and BMI using two-tailed test at 0.05 level of significance.
  4. Multiple linear regression analysis was performed using a backward step-wise elimination model, to determine if BMI was an independent determinant of functional disability and to control for confounding variables.



  Results Top


Baseline characteristics

The sociodemographic characteristics of the 140 patients recruited for the study is as shown in [Table 1].
Table 1 Summary of the demographic characteristics of knee osteoarthritis patients (N = 140)

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One hundred and twenty (85.7%) of the patients were female and 20 (14.3%) were male. The female:male ratio was 6:1.

The mean age of the patients was 59.6 (±8.8) years. The mean ages for male and female patients were 61.3 (±6.3) and 59.6 (±8.8) years, respectively. The modal age group was 50 to 59 years.

Anthropometric parameters

The mean BMI of the patients was 30.5 ± 6.4 kg/m2. The mean BMI of female and male patients was 31.1 ± 6.4 and 27.1 ± 4.2, respectively. Female patients were more obese than male patients (31.1 ± 6.4 vs. 27.1 ± 4.2, P = 0.008).

The distribution of BMI among patients is as shown in [Figure 1]. Twenty-seven patients (19.3%), comprising 15 females and 12 males, had normal weight; 45 patients (32.1%) comprising 40 females and five males were overweight, whereas 68 (49.6%) patients, comprising 65 females and three male patients, had various classes of obesity. BMI was higher among patients of age less than 60 years compared to those aged 60 years and above (32.5 ± 6.9 vs. 28.4 ± 4.8, P = 0.000).
Figure 1 Distribution of BMI in patients with knee osteoarthritis

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The range of waist circumferences was 58 to 125 cm, and the mean waist circumference was 91.9 ± 12 cm. The range of hip circumference of the patients was 74 to 138 cm, with a mean of 102.4 ± 12.7 cm.

The mean waist–hip ratio was 0.9 ± 0.1, with a range of 0.73 to 1.0. The mean waist–hip ratios for male and female patients were 0.95 ± 0.06 and 0.87 ± 0.06, respectively, with the gender disparity in waist–hip ratio being significant (t = 4.596, P = 0.000).

Analysis of self-reported knee pain

The distribution of knee OA pain is as shown in [Table 2]. All patients had knee pain during daily activities that necessitated their presentation at the rheumatology clinic. Mean duration of knee pain was with 3.5 (±2.9) years, with a range of 4 weeks to 20 years.
Table 2 Showing the summary of clinical features in patients with knee osteoarthritis

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One hundred and twenty (85.7%) patients had bilateral knee pain, whereas 20 (14.3%) patients had unilateral knee pain. Ninety-eight (70%) patients reported that the right knee was the most symptomatic (index knee), whereas 42 patients (30%) reported that the left knee was the most symptomatic (index knee).

The mean duration of knee pain in obese/overweight patients was 3.91 ± 4.8, whereas the mean duration of knee pain in those with normal BMI was 3.12 ± 2.7. There was no significant difference in the mean duration of knee pain between obese and nonobese patients (3.91 ± 4.8 vs. 3.12 ± 2.7, P = 0.23).

There was also no significant difference in the mean duration of knee pain between male and female patients (2.02 ± 2.29 vs. 3.75 ± 4.01, P = 0.064).

The overall distribution of WOMAC pain, stiffness, and disability subscales score is as shown in [Table 3]. The mean pain score using WOMAC pain subscale was 2.2 ± 0.7.
Table 3 Showing the overall scores for WOMAC index subscales of pain, stiffness, and functional disability

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The ordinal distribution of knee pain intensity in the patients is as shown in [Table 3]. Five patients (3.6%) had mild pain, 33 patients (23.6%) had moderate knee pain, 78 (55.7%) had severe pain, and 24 patients (17.1%) had extreme pain.

Mean pain score correlated strongly with mean functional disability score (r = 0.81, P = 0.000). Obese patients had higher mean pain score compared to nonobese patients (2.4 ± 0.78 vs. 1.93 ± 0.59, P = 0.00).

Analysis of self-reported functional disability

The mean disability score was 2.17 (±0.89), range was 0 to 4, and median score was 2.21.

Fifteen (10.7%) patients had no functional disability, 19 (13.6%) patients had mild functional disability, 81 (57.9%) had moderate disability, 21 (15%) patients had severe disability, and four (2.5%) patients had extreme disability.

The results of self-reported tasks difficulties by patients are as shown in [Table 4].
Table 4 WOMAC functional disability score analysis by specific task presented as mean, median, and standard deviation

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Knee OA patients had more difficulties with activities that involved movement of the knees as opposed to activities that can be achieved with the knees in resting position, as evident by higher mean and median disability scores in the former. Greater difficulty was reported with ascending stairs (2.6 ± 1.0), descending stairs (2.5 ± 1.0), heavy domestic duties (2.6 ± 1.0), bending to the floor (2.5 ± 1.1). Least difficulty was reported for lying on bed (1.8 ± 1.0), taking off socks (1.8 ± 1.0), and sitting (1.9 ± 0.9).

Overall, women had higher functional disability scores compared to men (2.3 ± 0.9 vs. 1.7 ± 0.7, P = 0.006).

Obese patients had higher disability scores compared to nonobese patients (2.58 ± 0.79 vs. 1.78 ± 0.81, P = 0.000).

BMI showed moderate positive correlation with functional disability (r = 0.5, P = 0.000). The duration of knee pain correlated weakly with functional disability (r = 0.26, P = 0.002).

Age showed a nonsignificant inverse correlation with functional disability (r = −0.56, P = 0.52); BMI may be a confounder here, as BMI was higher in patients aged less than 60 years when compared to the elderly patients (<60 vs. >60 years: 32.5 ± 6.9 vs. 28.3 ± 4.8, P = 0.000). Results of multilinear regression analysis is as depicted in [Table 5] and [Table 6]. Obesity is an independent risk factor for functional disability in patients with knee OA.
Table 5 Model summary for multilinear regression

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Table 6 Coefficient of multilinear regression

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  Discussion Top


Knee OA is a highly prevalent condition associated frequently with functional disability and consequent high direct and indirect cost.[3],[4] An increase in the incidence and prevalence of this condition is projected with an expected increase in life expectancy and population age.[23],[24] Hence, understanding the factors that are predictive of functional disability is clearly needed and of high priority especially in the setting of paucity of local studies in the Northern part of Nigeria.

The demographic characteristics of the patients in this study have similarities and differences with previous studies performed in south west Nigeria that are worth highlighting. The patients in this study are older (range = 45–80, mean ± SD = 59.61 ± 8.8) and predominantly female (M:F = 1:6), with only seven (6.3%) of the patients being under 50 years of age. Although confirming earlier studies which showed that knee OA is a disease of those of middle to elderly age,[3],[14],[25] this study contrasts with the study performed by Ebong[13] in Ibadan, which showed a mean age of 52 years with 39.5% of the patients being under 50 years of age. Studies done on knee OA patients shown gender disparity in favor of female, with a gender ratio range of 2:1 to 3:1 (F:M).[13],[14],[25] Recent studies by Adelowo and Oguntona[4] showed a high gender ratio of 4.6:1 (F:M) among OA patients. Higher prevalence of obesity in females compared to males[11] is the most likely reason for the gender disparity in knee OA. The higher gender disparity in this study could also be due to the higher mean age of the patients, given that the incidence and prevalence of knee OA increases markedly in female after the 5th decade of life, a fact that has been adduced to the loss of the protective anti-inflammatory effect of estrogen with the onset of menopause.[26] It is also possible that difference in health seeking behavior between male and female is partly responsible for the wide gender disparity noted in this study.

The mean BMI of the study patients was in the obese range (30.5 ± 6.3 kg/m2), with only 19.2% of the patients having normal weight, the rest 87.8% being either overweight (32.2%) or obese (48.6%). The high prevalence of obesity in this study is supported by recent studies where the prevalence of obesity was noted to be high in patients with OA,[26],[27],[28],[29] but in contrast with earlier Nigerian studies on arthritis patients which showed less than 10% prevalence of obesity.[3],[25] This wide disparity may be reflective of an increasing prevalence of obesity among the Nigerian populace in keeping with global obesity epidemic, given changing lifestyle and dietary habits. It is noteworthy that prevalence of obesity in this cohort (48.6%) is higher than 8.1% to 22.2% prevalence range of obesity found in systemic review of community-based studies of Nigerians, with obesity consistently occurring more in females than males.[11] Although this study is not designed to determine the cause–effect relationship between obesity and knee OA, the occurrence of obesity in almost 50% of knee OA could be a pointer to etiological role of obesity in causation of knee OA. More importantly, the high prevalence of obesity among Nigerian knee OA patients does poses a risk for disease severity and progression and compounds management challenge.The occurrence of high mean pain score in overweight/obese knee OA patients compared to those normal BMI is in conformity with findings in studies from other climes that showed increased pain severity in obese patients.[26],[27],[28] Likewise, the higher functional disability scores in obese Nigerian knee OA compared to those with normal BMI is in keeping with findings from earlier studies that have shown that knee OA in the setting of obesity is particularly associated with severe functional limitation.[26],[27],[28],[29] Worse still, obesity is a predictor of high radiographic score as a result of increased joint damage and accelerated disease progression.[26],[30],[31],[32] Though it is difficult to establish a cause–effect relationship between obesity and functional disability in a cross-sectional study, there is a consensus among studies that obesity is a strong predictor of functional disability.[26],[30] This should, however, present an opportunity for better patient management as strategies designed to prevent or reduce obesity in knee OA patients will impact positively on pain, functional disability, reduce the risk of metabolic syndrome, and improve the general well-being of these patients.[33]


  Conclusion Top


Pain and functional disability are more severe in obese Nigerian knee OA patients compared to those with nonobese patients, and obesity is an independent predictor of functional disability among Nigerian knee OA patients.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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